A transfer robot for transporting a substrate such as a semiconductor wafer, a glass substrate, or the like has at its distal end an end effector (for example, a hand). The transfer robot is configured such that it holds and transports a substrate using the hand. As an example of the hand for holding a substrate, there can be cited a hand which is configured to hold a substrate by applying suction to an underside of the substrate. In such a type of hand, however, particles may adhere to the substrate's underside at the time of suction. The adhering of particles to a substrate is objectionable. It is therefore preferable to hold a substrate using a different technique preventing adhesion of particles. As a method preventing adhesion of particles, there can be cited a technique of gripping a substrate. As a hand capable of implementing such a technique, there can be cited a blade as set forth, for example, in Patent Literature 1.
The blade as set forth in Japanese Laid-Open Patent Application Publication No. 2002-134586 is formed into a Y-shape and has a joint to which an arm of a robot is coupled. A mounting wing is attached to the joint such that it extends from the joint. The mounting wing is formed such that it is bifurcated on its end side into two ends and there is formed at each end a fixing fin.
In addition, the joint is provided with a clamping member for clamping a substrate on the mounting wing. The clamping member has a moving pusher and a pneumatic cylinder. The pneumatic cylinder serves to advance and retract the moving pusher. The moving pusher is configured such that its forward movement pushes the substrate on the mounting wing in the direction of the fixing fins to thereby support, along with the fixing fins, the substrate.
The clamping member thus configured further has a spring for shock protection. This shock protection spring is mounted in the moving pusher and serves to reduce the shock imparted from the moving pusher to the substrate upon contact of the moving pusher with the substrate.
The blade as set forth in Japanese Laid-Open Patent Application Publication No. 2002-134586 is configured such that the moving pusher is moved forward by the pneumatic cylinder to abut against the substrate to thereby support it. Therefore, at the time when the moving pusher is brought into abutment with the substrate, a shock is applied to the substrate from the moving pusher. In order to reduce the shock, the moving pusher is provided with the shock protection spring.
In spite of the fact that a shock protection spring can reduce shock, damping characteristic of the spring occurs because of its large bounce. If damping takes place, the pressing-force with which the moving pusher pushes a substrate becomes unstable and the substrate will no longer be held firmly. Therefore, it is not until the damping of the shock protection spring subsides after abutment of the moving pusher with the substrate that the blade is finally allowed to move. This increases the length of time during which the substrate is to be gripped.